110. Balanced Binary Tree.md

110. Balanced Binary Tree

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leetcode-cn Daily Challenge on August 17th, 2020.

leetcode Daily Challenge on December 22th, 2020.

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Difficulty : Easy

Related Topics : Tree、DFS

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Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the left and right subtrees of every node differ in height by no more than 1.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7
Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
Return false.

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Solution

• mine
  • Java
    • DFS Runtime: 0 ms, faster than 100.00%, Memory Usage: 39.6 MB, less than 71.59% of Java online submissions

      //O(N)time
      //O(D)space
      boolean res = true;
      public boolean isBalanced(TreeNode root) {
          dfs(root);
          return res;
      }
      
      int dfs(TreeNode node){
          if(node == null || !res) return 0;
          int left  = dfs(node.left);
          int right  = dfs(node.right);
          if(Math.abs(left - right) > 1){
              res = false;
          }
          return Math.max(left, right) + 1;
      }
      

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